Controlled wide spectrum compact ultrabrief laser source

ABSTRACT

The invention concerns a wide spectrum ultrashort compact laser source including a laser primary source ( 6 ) with rare earth ions. This source ( 6 ) is pumped by a luminous pump flux ( 9 ) centred on a wavelength λ D , said flux ( 9 ) being emitted by a solid laser pump source ( 8 ). The primary source ( 6 ) emits a primary luminous flux ( 7 ) centred on a wavelength λ L  of spectral width Δλ L . The latter is injected by means of injection optics ( 10 ) into a photonic crystal fibre ( 2 ) having a length L, a section d, and a set of cavities ( 4 ) of diameter φ. Coupling optics ( 15 ) collect the luminous flux ( 12 ) at the output of the fibre with phonic crystals ( 2 ). This luminous flux ( 12 ) is centred on a wavelength λ F  and has a spectral width Δλ F . The spectrum is subjected inside the photonic crystal fibre ( 2 ) to a widening due for more than  50 % of the phase self-modulation.

This invention concerns a controlled wide spectrum ultrashort compactlaser source.

Since the realisation by Ippen and Shank in 1974 [Appl. Phys. Letters;24, (1974) 373] of the first laser emitting pulses shorter than thepicosecond (1 ps=10⁻¹² s), the duration of laser pulses has been reducedfurther and further. Lasers generating pulses whereof the duration issmaller than the picosecond are designated as “Ultrashort lasers”. Theyattract strong interest and intense research endeavours in thescientific community because the ultrashort pulses generated enabletemporal study of the dynamics of ultrarapid processes (smaller than10¹⁰ s) inaccessible until now for most detectors. With these ultrashortlight sources, new fields of investigations and applications appear, asin the process of fragmentation and/or desorption of multiphotonicadsorbed molecules, metrology, non-destructive studies of chemicalmechanisms in biological cells, etc.

The generation of wide spectral band ultrashort optical signals hasbecome a routine. Lasers using as an amplifying medium a titanium-dopedsapphire crystal (Ti⁺³:Al₂O₃) and available commercially generate pulseshaving a duration close to 10 fs (1 fs=10⁻¹⁵ s) which corresponds to aspectral width of the order of 100 THz (1 THz=10¹² Hz). These pulses arevastly tunable by modifying or adjusting the laser resonator. However,the operation of lasers using the titanium-doped sapphire requires anindependent pump laser source. This source is generally an ionic laser(Argon) or an Nd:YAG laser pumped by diodes and frequency-doubled. Thisindependent pump laser source is rather detrimental to the spacerequirements of the laser system and the reliability of the equipment.Moreover, this source makes the total cost of an ultrashort laser systemrelatively high.

Besides, lasers generating ultrashort pulses involving amplifying mediawith rare earth ions (Ytterbium (Yb), Neodymium (Nd), . . . ) are known.Such lasers may advantageously be pumped directly by a junction laser.They show, therefore, very attractive characteristics since they arecompact, reliable and cheap. However, the fluorescence width of suchlaser media limits strongly the spectrum of the pulse emitted andconsequently the spectral range over which the laser is tunable.Typically, for a Yb:YAG laser, the fluorescence width is 6 nm (1 nm=10⁻⁹m), the spectral width is approximately 3 nm and it is not easilytunable. These figures should be compared with those of the laser usingthe titanium-doped sapphire which has a fluorescence width of 200 nm, aspectral width greater than 100 nm and a tunability range between 750and 950 nm.

In the U.S. Pat. No. 6,097,870, Ranka and al. have shown the possibilityof realising the spectral widening of a pulsed luminous flux byimplementing a fibre with photonic crystals. The pulses injected intosaid fibre, 75 cm long, are generated by a laser source and are definedby a peak power greater than a few hundred watts. Thus, by being coupledin a fibre with photonic crystals, the generated spectrum is as wide aspossible and the mechanisms responsible for this widening are the phaseself-modulation, the stimulated Raman emission, the parametricamplification, the 4-wave mixture and the creation of an optical shockwave. Still, these physical mechanisms are not all understood and thewidening of the spectrum is not controllable, as regards its amplitudeas well as its spectral width. Consequently, it is not possible tooptimise the widening conditions of said spectrum in order to select,using a filter, a particular pass-band having a maximised intensity.

The purpose of this invention is to provide an ultrashort laser sourcesimple in its design and in its operating mode, compact, cheap andenabling to obtain pulses with controlled wide spectrum, in width aswell as in their intensity-related spectral distribution.

To this end, the invention concerns a wide spectrum ultrashort lasersource including:

-   -   a laser primary source with rare earth ions receiving a luminous        pump flux centred on a wavelength λ_(D), said flux being emitted        by a solid laser pump source, said primary source including an        active material and emitting a primary luminous flux centred on        a wavelength λ_(L) of spectral width Δλ_(L).    -   a photonic crystal fibre having a length L, a section d, and a        set of cavities of diameter φ,    -   injection optics sending the primary luminous flux emitted by        the primary source into the fibre with photonic crystals,    -   coupling optics collecting the luminous flux at the output of        the fibre with photonic crystals, said flux being centred on a        wavelength λ_(F) and of spectral width Δλ_(F).

According to the invention, the spectrum is subjected inside thephotonic crystal fibre to a widening due for more than 50% of the phaseself-modulation.

In different possible embodiments, this invention also concerns thecharacteristics which will appear during the following description andwhich should be considered individually or in all their technicallypossible combinations:

-   -   the contribution to the widening of the spectrum of the phase        self-modulation is preferably greater than 80%,    -   the length L of the photonic crystal fibre verifies 5≦L≦40 cm        and the power density of the incident primary luminous flux is        smaller than 600 Gigawatts/cm²,    -   it includes a wavelength selection device,    -   the wavelength selection device comprises a grid of        interferential filters,    -   said flux of spectral width Δλ_(F) exhibits amplitude        modulations of average period τ and the pass-band of each filter        is adapted to this average period τ,    -   the solid laser pump source is a junction laser,    -   the active material comprises ytterbium ions,    -   the active material comprises neodymium ions,    -   the spectral width Δλ_(F) ranges between 10 and 400 nm,    -   the diameter φ of the cavities, the length L and the section d        of the fibre with photonic crystals, the spacing between the        cavities are selected so that the dispersion of the primary        luminous flux centred on the wavelength λ_(L) in said photonic        crystal fibre is in absolute value smaller than the dispersion        of a homogeneous optic fibre of the same material and of length        L for the wavelength λ_(L),    -   the dispersion of the primary luminous flux centred on the        wavelength λ_(L) in the photonic crystal fibre is nil.

The invention also concerns a sample measuring device usingmultiphotonic confocal microscopy comprising:

-   -   a confocal microscope including a lens,    -   a light source emitting a luminous flux,    -   means capable of directing said luminous flux to a sample        through the microscope,    -   means for detecting the intensity of the luminous flux produced        by the interaction of the luminous beam emitted by the light        source on the sample and collected by the microscope,    -   means for processing the signal produced by the means of        detection.

According to the invention, the light source comprises:

-   -   a laser primary source with rare earth ions receiving a luminous        pump flux centred on a wavelength λ_(D), said flux being emitted        by a solid laser pump source, said primary source including an        active material and emitting a primary luminous flux centred on        a wavelength λ_(L) of spectral width Δλ_(L),    -   a photonic crystal fibre having a length L, a section d, and a        set of cavities of diameter φ,    -   injection optics sending the primary luminous flux emitted by        the primary source into the fibre with photonic crystals,    -   coupling optics collecting the luminous flux at the output of        the fibre with photonic crystals, said flux being centred on a        wavelength λ_(F) and of spectral width Δλ_(F).

In different possible embodiments, this invention also concerns thecharacteristics which will appear during the following description andwhich should be considered individually or in all their technicallypossible combinations:

-   -   the spectrum is subjected inside the photonic crystal fibre to a        widening due for more than 50% of the phase self-modulation,    -   the contribution to the widening of the spectrum of the phase        self-modulation is preferably greater than 80%,    -   the length L of the photonic crystal fibre verifies 5≦L≦40 cm        and the power density of the primary luminous flux incident is        smaller than 600 Gigawatts/cm².

The invention will be described more in detail with reference to theappended drawings whereon:

FIG. 1 is a diagrammatic representation of an ultrashort laser source,according to the invention;

FIG. 2 is a diagrammatic representation of a photonic crystal fibrewherein is injected the luminous flux emitted by the primary lasersource, according to the invention;

FIG. 3 shows the spectral distribution of the intensity of a luminousbeam at the output of a photonic crystal fibre for a peak power of theprimary luminous flux of 80 kW, according to an embodiment of theinvention;

FIG. 4 represents the spectral width Δλ_(F) of a luminous flux at theoutput of a photonic crystal fibre relative to the peak power of anincident primary luminous flux, in an embodiment of the invention.

The purpose of the invention is a controlled spectral widening of aluminous flux generated by a laser source, obtained by optimisation ofthe experimental parameters (power of the laser source, core diameter ofthe fibre, length of the fibre), so that the phase self-modulation ismainly responsible for the spectral widening, and not the other physicalprocesses also noted in the generation of supercontinuum (stimulatedRaman emission, parametric amplification, 4-wave mixture, etc.).

The wide spectrum ultrashort laser source of the invention associates alaser source 1 using rare earth ions with an optic photonic crystalfibre 2. This photonic crystal fibre 2 is a fibre 3 advantageously ofsilicium having a periodic grid of cavities 4 conferring particularoptical properties thereto. It is thus possible to widen the spectrum ofa luminous flux introduced therein quite significantly. Such widening,according to the invention, is due for more than 50%, and preferably formore than 80%, to the phase self-modulation. A set of wavelength filters5 then enables if necessary to select a particular emission wavelength.The ultrashort laser source includes a primary source 6. By primarysource is meant an ultrashort laser source with rare earth ions. Thisprimary source 6 emits a primary luminous flux 7 centred on a wavelengthλ_(L) of spectral width Δλ_(L). λ_(L) ranges typically between 1000 and1100 nm and Δλ_(L) is typically of the order of a few nm. The primarysource 6 includes an active material pumped by a pump laser source 8.This pump laser source 8 is a solid laser emitting a luminous pump flux9 centred on a wavelength λ_(D). In a preferred embodiment, the pumplaser source 8 is a junction laser. The wavelength λ_(D) whereon iscentred the luminous pump flux 9 ranges typically between 800 nm and 1μm. The rare earth ions used in the active material of the primarysource are selected among one of the following materials: Ytterbium(Yb), Neodymium (Nd) or any equivalent material.

The ultrashort laser source also comprises injection optics 10 sendingthe primary luminous flux 7 centred on a wavelength λ_(L) and emitted bythe laser primary source 6 in a photonic crystal fibre 2. For nonlimiting exemplification purposes, these injection optics 10 include atleast one lens. The photonic crystal fibre 2 has a length L and asection d. preferably, the length L of the photonic crystal fibre 2verifies 5≦L≦40 cm. The photonic crystal fibre 2 comprises a periodicgrid of cavities 4 of diameter φ which are holes filled with air runningthrough the whole length L of said fibre 2. Advantageously, the core ofthe photonic crystal fibre 2 does not include any additional cavities11. In a preferred embodiment, the photonic crystal fibre 2 is made ofsilicium. In another embodiment, the material forming the photoniccrystal fibre 2 is glass or any other equivalent material. In anembodiment, the geometry and the diameter of these cavities 4 as well asthe length and the section d of the photonic crystal fibre 2 areselected so that the fibre 2 shows a dispersion in absolute valuesmaller than the dispersion of a homogeneous optic fibre of the samematerial and of length L for the wavelength λ_(L). In the case ofsilicium, for example, the dispersion is in absolute value smaller than40 ps/km/nm at a wavelength λ_(L)=1025 nm. Preferably, the geometry andthe diameter of the cavities 4 as well as the length and the section dof the photonic crystal fibre 2 are selected so that the fibre 2 showszero dispersion for the wavelength λ_(L). It is then possible to obtainan extremely great spectral widening of the primary luminous flux 7.This widening remains very significant even for a primary luminous flux7 exhibiting limited peak power. Advantageously, the power density ofthe primary luminous flux 7 is smaller than 600 Gigawatts/cm².

At the output of the photonic crystal fibre 2, the spectral width Δλ_(F)of the luminous flux 12 ranges between 10 and 400 nm. It extendstherefore maximum between 900 and 1300 nm and typically between 950 and1150 nm. This spectral widening is centred on a wavelength λ_(F) and alocation on either side of the wavelength λ_(L).

FIG. 3 shows the spectral distribution of the intensity at the output ofa photonic crystal fibre 2 for a peak power of the primary luminous flux7 equal to 80 kW. The photonic crystal fibre 2 is 10 cm long and has acore of diameter φ=5.5 μm. The axis of abscisses 13 represents thewavelength, in nanometres (nm), and the axis of ordinates 14 theintensity, in arbitrary units, of the luminous flux 12 at the output ofthe photonic crystal fibre 2. The spectral support of the widenedspectrum is perfectly delineated between 950 nm and approximately 1110nm. This intensity spectral distribution exhibits amplitude modulationshaving an average period τ. By “average period” is meant the average ofthe periods of the amplitude modulations observed in the spectrum.

Coupling optics 15 are placed at the output of the fibre 2 with photoniccrystals in order to collect the luminous flux 12. This luminous flux 12is centred on a wavelength λ_(F) and has a spectral width Δλ_(F).Advantageously, the ultrashort laser source includes a wavelengthselection device 5. At the output of this selection device 5, theluminous flux emitted by the laser source is centred on a wavelengthλ_(s) and has a spectral width Δλ_(s). The pass-band of each filter usedis advantageously adapted to the average period τ of the modulations ofthe spectrum of width Δλ_(F) of the luminous flux 12 (FIG. 3).

In a preferred embodiment, the wavelength selection device 5 comprises agrid of interferential filters. The wavelength tunability is forinstance obtained by rotation of the interferential filter, in order tomodify the angle of incidence of the wide spectrum beam 12 on thefilter. It is possible, in particular, to optimise the wideningconditions in order to adjust the maxima of the spectrum of FIG. 3, sothat they match the maximum transmission wavelengths of the filters.

A theoretical approach has been developed in order to explain thespectral widening observed of the primary luminous flux 7 injected intothe photonic crystal fibre 2. According to this theory, the cavities 4form a periodic grid of defects creating a forbidden photonic band inthe fibre 2. Electromagnetic modes having frequencies comprised in saidforbidden band may then propagate along these defects. The length of thephotonic crystal fibre is sufficiently short and the power density ofthe primary luminous flux 7 injected into the photonic crystal fibre 2is such that the non-linear effects are mainly due to the phaseself-modulation. These non-linear effects accumulate throughout thepropagation of said primary luminous flux 7 to lead to a spectralwidening. The other physical processes generally observed in thegeneration of the supercontinuum such as the stimulated Raman emission,the parametric amplification, the four-wave mixture and the opticalshock wave contribute only marginally to the spectral widening.

In the case of a widening solely related to the phase self-modulation,the phase of an ultrashort luminous pulse propagating in a non-linearmedium such as an optic fibre depends on the intensity by the relation:${\Delta\quad{\Phi(t)}} = {\frac{2\pi}{\lambda}n_{2}{I(t)}L}$where λ is the wavelength of the pulse, n₂ the non-linear index of thepropagation medium, I(t) the luminous intensity at the instant t, and Lthe length of the material traversed.

The associated frequency variation is then given by:${\Delta\quad{\omega(t)}} = {{- \omega_{0}}\frac{n_{2}L}{c}\frac{\mathbb{d}{I(t)}}{\mathbb{d}t}}$and the spectrum of the corresponding pulse is then given by the Fouriertransform as the function A(ν):Δω(ν)=TF[A(ν)]

In an embodiment, FIG. 4 shows the width of the spectrum relative to thepeak power of the primary luminous flux for a photonic crystal fibre 2of length 10 cm and having a core of diameter φ=5.5 μm. The axis ofordinates 17 represents the spectral width Δλ_(F), in nm, of theluminous flux 12 at the output of the photonic crystal fibre 2 and theaxis of abscisses 16 represents the incident power, in kWatt, of theprimary luminous flux 7 injected into said fibre. The measuring points18 correspond to experimental measurements carried out for given peakpower values of the primary luminous flux 7. The uncertainties on themeasured value of the spectral width Δλ_(F) have been plotted on Figureby error bars. The profile 19 (full line) is the result of a modellingof the widening solely related to the phase self-modulation and whereofthe model has been described above. As an example and within theuncertainty values, for an incident peak power of 80 kW, the value ofthe measuring point is greater by approximately 10% than the value ofthe spectral widening obtained by the model describing the phaseself-modulation.

The invention also concerns a sample measuring device by multiphotonicconfocal microscopy. The arrangement comprises a microscope including alens and an ultrashort laser source, emitting an energization luminousflux centred on a wavelength λ_(s) and of spectral width Δλ_(s). Thisultrashort laser source comprises a laser primary source 6 with rareearth ions receiving a luminous pump flux 9 emitted by a solid laserpump source 8. This primary source 6 includes an active material andemits a primary luminous flux 7 centred on a wavelength λ_(L) ofspectral width Δλ_(L). Injection optics 10 send the primary luminousflux 7 emitted by the primary source 6 into a photonic crystal fibre 2and coupling optics 15 collect the luminous flux 12 at the output ofthis photonic crystal fibre 2. In a preferred embodiment, the spectrumis subjected inside the photonic crystal fibre 2 to a widening due formore than 50% of the phase self-modulation. The contribution to thespectral widening of the phase self-modulation is preferably greaterthan 80% Means capable of directing said energization luminous flux sendsaid flux to a sample through the microscope. Advantageously, the sampleis placed in the focal plane of the lens. The interaction of theenergization luminous flux with the sample to be analysed creates ananalysis confocal volume. Means ensure the detection of the intensity ofthe luminous flux produced by the interaction of the energizationluminous flux centred on the wavelength λ_(s) with the sample andcollected by the microscope. These means comprise advantageously CCDsensors or photomultipliers. Means of processing enable to analyse thesignal produced by the means of detection.

Associated with the spatial resolution of the confocal microscope, theuse of ultrashort duration luminous flux enables, according to anembodiment, to study cellular chemical phenomena in vivo. The luminousflux detected is in an embodiment a luminescent flux produced by theinteresting particles in the confocal volume. This luminescent fluxresults from the fluorescence generated by the absorption caused by theinteresting particles of at least two photons. Its density issignificant only in the extremely reduced spatial extension analysisconfocal volume. The possible deterioration of the sample is therebylimited.

Moreover, the sample measuring device using multiphotonic confocalmicroscopy exhibits the following advantages or may advantageously beimplemented in the following cases:

1) Wavelength Range Available

Implementing a laser source that is tunable in the 1000-1200 nm rangeprovides interesting advantages in the field of the multi-photonmicroscopy. To optimise the efficiency of the imaging process, thelargest number of photons derived from the laser source should becoupled at cellular level. Two phenomena contribute to the degradationin efficiency of such coupling. Namely, the diffusion in the biologicaltissue, significant at short wavelengths, and the absorption of water,significant at wavelengths greater than 1300 nm.

The wavelength range of the tunable laser source corresponds to acompromise which maximises the coupling efficiency.

2) Multi-Wavelength Simultaneous Measurement

The laser sources used traditionally in multiphotonic microscopy aresources tunable over the 750-1000 nm range. These sources cannottransmit several wavelengths simultaneously, the fluorescencemeasurement on different fluorochromes, whereof the energizationspectral domain is different, can only be sequential. Consequently, afirst measurement must be performed at a wavelength λ₁, then theemission wavelength of the laser should be modified in order to conducta second measurement at a wavelength λ₂, and so on and so forth. By“fluorochrome” is meant any molecule liable to be energized at a givenwavelength λ_(i) and to emit a luminous flux centred on a wavelengthλ_(j).

The sample measuring device using multiphotonic confocal microscopyenables advantageously simultaneous fluorescence measurement ofdifferent fluorochromes whereof the energization spectrum is different.

3) Possible Usage of New Fluorochromes

The laser source also enables to energize the fluorescence offluorochromes emitting in the red portion of the visible spectrum,possibly the near-infrared. The energization spectrum of thesefluorochromes is not compatible with the traditional sources.

4) Improvement of the Noise Produced by Self-Fluorescence

Measuring the fluorescence emitted by the fluorochromes is often madedifficult by the presence of other naturally fluorescent species in thebiological tissue. This spurious fluorescence, also calledself-fluorescence, reduces considerably the signal/noise ratio of themeasurement.

The table below specifies the main sources of self-fluorescence, as wellas the associated energization wavelengths (Biophotonics International8; N° 7 (2001) p 42). Source of self-fluorescence Energizationwavelength (nm) Flavins 380-490 NADH and NADPH 360-390 Lipofuscins360-490 AGE 320-370 Elastin and collagen 440-480 Lignin 488 Chlorophyll488

An energization wavelength greater than 1000 nm does not enable anyenergization caused by two-photon absorption at a wavelength smallerthan 500 nm. The self-fluorescent species cannot therefore be energizedby the laser source, object of the invention. The signal/noise ratiobetween the fluorescence of the fluorochrome and the noise generated byself-fluorescence is vastly improved, as well as the contrast of theimages realised by means of the microscope.

5) Possibility of FRET Measurements

The fluorescence resonance energy transfer (FRET) measurements implementfluorescence energy transfer between a fluorochrome donor and areceiver. A laser source energizes the fluorescence of the donor, andthe fluorescence of the donor energizes that of the receiver.

The absorption and emission spectra of the donor and of the receiverfrequently overlap one another. The sample measuring device usingmultiphotonic confocal microscopy enables simultaneous energization ofthe donor and of the receiver for calibration and control purposes.

6) Usage in Multiphotonic Microscopy

The usage of the sample measuring device using multiphotonic confocalmicroscopy enables to energise numerous fluorochromes by three-photonabsorption, and not by two-photon absorption. The confocal volumewherein the fluorescence may take place is substantially smaller in thecase of the three-photon absorption, compared with the case of thetwo-photon absorption. The spatial resolution of the measurement is thusvastly improved.

1-16. (cancelled)
 17. A wide spectrum compact ultrashort laser sourceincluding: a laser primary source (6) with rare earth ions receiving aluminous pump flux (9) centered on a wavelength λ_(D), said flux (9)being emitted by a solid laser pump source (8), said primary source (6)including an active material and emitting a primary luminous flux (7)centered on a wavelength XL of spectral width Δλ_(L), a photonic crystalfiber (2) having a length L, a section d, and a set of cavities (4) ofdiameter φ, injection optics (10) sending the primary luminous flux (7)emitted by the primary source (6) into the photonic crystal fiber (2),coupling optics (15) collecting the luminous flux (12) at the output ofthe photonic crystal fiber (2), said flux (12) being centered on awavelength λ_(F) and of spectral width Δλ_(F), characterized in that thespectrum is subjected inside the photonic crystal fiber (2) to awidening due for more than 50% of the phase self-modulation.
 18. A widespectrum ultrashort laser source according to claim 17, characterized inthat the contribution to the widening of the spectrum of the phaseself-modulation is preferably greater than 80%.
 19. A wide spectrumultrashort laser source according to claim 17, characterized in that thelength L of the photonic crystal fiber (2) verifies 5≦L≦40 cm and thepower density of the primary luminous flux (7) incident is smaller than600 Gigawatts/cm².
 20. A wide spectrum ultrashort laser source accordingto claim 17, characterized in that it includes a wavelength selectiondevice (5).
 21. A wide spectrum ultrashort laser source according toclaim 20, characterized in that the wavelength selection device (5)comprises a grid of interferential filters.
 22. A wide spectrumultrashort laser source according to claim 21, characterized in thatsaid flux (12) of spectral width Δλ_(F) exhibits amplitude modulationsof average period τ and that the pass-band of each filter is adapted tothis average period τ.
 23. A wide spectrum ultrashort laser sourceaccording to claim 17, characterized in that the solid laser pump source(8) is a junction laser.
 24. A wide spectrum ultrashort laser sourceaccording to claim 17, characterized in that the active materialcomprises ytterbium ions.
 25. A wide spectrum ultrashort laser sourceaccording to claim 17, characterized in that the active materialcomprises neodymium ions.
 26. A wide spectrum ultrashort laser sourceaccording to claim 17, characterized in that the spectral width Δλ_(F)ranges between 10 and 400 nm.
 27. A wide spectrum ultrashort lasersource according to claim 17, characterized in that the diameter φ ofthe cavities (4), the length L and the section d of the photonic crystalfiber (2), the spacing between the cavities (4) are selected so that thedispersion of the primary luminous flux (7) centered on the wavelengthλ_(L) in said photonic crystal fiber (2) is in absolute value smallerthan the dispersion of a homogeneous optic fiber of the same materialand of length L for the wavelength λ_(L).
 28. A wide spectrum ultrashortlaser source according to claim 27, characterized in that the dispersionof the primary luminous flux (7) centered on the wavelength λ_(L) in thephotonic crystal fiber (2) is nil.
 29. A sample measuring device usingmultiphotonic confocal microscopy comprising: a confocal microscopeincluding a lens, a light source emitting a luminous flux, means capableof directing said luminous flux to a sample through the microscope,means for detecting the intensity of the luminous flux produced by theinteraction of the luminous beam emitted by the light source on thesample and collected by the microscope, means for processing the signalproduced by the means of detection, characterized in that the lightsource comprises: a laser primary source (6) with rare earth ionsreceiving a luminous pump flux (9) centered on a wavelength λ_(D), saidflux (9) being emitted by a solid laser pump source (8), said primarysource (6) including an active material and emitting a primary luminousflux (7) centered on a wavelength λ_(L) of spectral width Δλ_(L), aphotonic crystal fiber (2) having a length L, a section d, and a set ofcavities (4) of diameter φ, injection optics (10) sending the primaryluminous flux (7) emitted by the primary source (6) in the photoniccrystal fiber (2), coupling optics (15) collecting the luminous flux(12) at the output of the photonic crystal fiber (2), said flux (12)being centered on a wavelength λ_(F) and of spectral width Δλ_(F), andin that the spectrum is subjected inside the photonic crystal fiber (2)to a widening due for more than 50% of the phase self-modulation.
 30. Asample measuring device using multiphotonic confocal microscopyaccording to claim 29, characterized in that the contribution to thewidening of the spectrum of the phase self-modulation is preferablygreater than 80%.
 31. A sample measuring device using multiphotonicconfocal microscopy according to claim 29, characterized in that thelength L of the photonic crystal fiber (2) verifies 5≦L≦40 cm and thepower density of the incident primary luminous flux (7) is smaller than600 Gigawatts/cm².
 32. A sample measuring device using multiphotonicconfocal microscopy according to claim 30, characterized in that thelength L of the photonic crystal fibre (2) verifies 5≦L≦40 cm and thepower density of the incident primary luminous flux (7) is smaller than600 Gigawatts/cm².